Dehumidifying the Garage?

[Alex Stokes]

Hi All,

It seems like it's been such a humid summer. My workshop is in my garage. I mostly leave the door down, but the lawnmower and motorcycle share the space. I had been thinking about getting a dehumidifier and leaving it in there to run. But... every time I open that door (daily) - I loose the advantage of doing that. It's an old one car garage attached tot the house. I put a good insulated garage door in last year, and insulated the space above, but the space isn't air conditioned either warm or cold. Any thoughts? I've got a rack of wood on the wall theoretically "drying", but I don't think much drying has gone on these last 6 months - lol

I picked up a dehumidifier yesterday intending to just let it run, but then I got to thinking about how often I open that garage door...

Anyway thoughts or is appreciated!

Alex

 

[jlimey]

If there isn't much temperature difference between the air in the garage and outside, you shouldn't experience much air exchange when you open the door. I would imagine that if you open the door, get out your bike and close it immediately, that a dehumidifier should be able to keep up (OK, maybe not to the setting that you have dialed in, but at least it would lower the humidity below ambient). Are you able to run a drain hose somewhere?

I have a two car garage with a window AC unit and have no trouble keeping the humidity to 40% with a dehumidifier. Of course, the AC helps.

 

[Charles Lent]

You should consider moving the mowers into their own small storage shed. Then you won't need to open the garage door as often. Once this problem is solved you can add a dehumidifier to your garage, but for about the same operating cost you could install a window air conditioner and it would dehumidify as well as cool your shop.

Charley

 

[Tarhead]

It takes a while (day's?) for any gain or loss of water from lumber. If you leave a dehumidifier cycling 24X7 you can open the door a few times/day and not worry. The largest water vapor contributor in most garages is the concrete floor... not humidity outside. If you want to make a big impact on humidity consider sealing the concrete floor if it's not already on top of a vapor barrier.

 

[Glennbear]

Just some thoughts based upon my experience, my previous shop in NJ was in my basement and high humidity was an issue during humid NJ summers. I rescued an old dehumidifier from the trash and that solved the problem. Here in VA I have a detached 24 x 24 garage/shop and a small window AC unit keeps humidity at a decent level while at the same time assuring that temps do not get so high that glues, finishes, etc are adversely affected.

 

[ehpoole]

It is definitely worth investing in a dehumidifier for the shop. Not only will it help stabilize wood moisture content from day-to-day (worth the effort in its own right IMHO) but it will also greatly reduce rusting of your tools and, particularly on muggy days, your shop will feel much more comfortable as sweat will actually be able to evaporate for a change! It will even make an air conditioned shop feel substantially more comfortable on humid days by further lowering the relative humidity levels since most of us only air condition our shops on those days we are in the shop.

While repeated openings of the garage door will certainly reduce the efficiency of your dehumidifier, it will still make a huge dent in the overall humidity provided you keep the door open for as short a duration as possible and upsize the dehumidifier with a higher capacity unit -- all that dry air does not disappear the instant you open the doors, save for windy days at least, opening the doors for a minute or two several times each day will not defeat the dehumidifier, it will just reduce efficiency by forcing it to work harder to overcome the influx of moist air. However, this usage pattern will reduce the effectiveness of it's rust inhibiting abilities since opening the door on a moist day when the shop is cooler than the outdoors will still allow moisture to momentarily condense on your (cast iron) tools.

When you go shopping you should opt for the larger 50 to 70 pint models and not their cheaper, lower capacity, siblings. The efficiency of a dehumidifier increases significantly with capacity (as in they will remove more moisture for the same KWH of electricity) and you will easily recover the difference in cost in the form of reduced electric bills over the life of the dehumidifier. I also recommend opting for models that have digital humidity settings and a hose and/or pump hookup that will allow you to setup your dehumidifier to automatically dispose of the accumulated condensate as repeatedly emptying the condensate bucket multiple times each day will grow old very fast. I use an external condensate pump to pump the condensate up and out one of my shop windows (which also has the A/C installed in it) and into the flower bed under the window, this way I never have to deal with emptying the condensate bucket and the dehumidifier runs entirely unattended. It could also have pumped the condensate into a utility sink or any other suitable drainage site.

Best of luck as a dehumidifier is well worth the investment IMHO!

 

[Alex Stokes]

Good points all, and thanks for taking the time to give me some things to ponder. I did see a nice little air-conditioning unit that stands in a fairly small piece of floor space over at Home Depot two days ago. If I ran the air conditioner, would I still need the dehumidifier? I'm guessing the answer is "probably" - I would only run the A/C on days I was out there working - and I'm a part time wood-worker. But the humidity would be an ongoing issue every day...)

Charley, I'm gonna get a shed built. It's just not this year. (I'm closely watching Canuck's progress on his and making notes).

Mark, I've heard in a few different places now that sealing the floor would be a good idea. But that seems like an awful lot of work? And it was expensive - last time I saw an offer/estimate. Is it really worth it? I have thought about it though. I think the original owner painted my garage floor gray when it was built - 40 years ago, and there's STILL gray paint coming up in a few spots! (sigh) (Bet it was lead based paint too!)

Ethan, I would agree that a 50 pint unit is probably a good choice for me. I like the idea of running the condensate out the window to water the roses. I have no drain points in my garage. Which type/brand of condensate pump did you pick? (I've never seen one)

Again, thanks for the advices my friends

Alex

 

[ehpoole]

Alex,

Yes, you will still need a dehumidifier even with air conditioning if you are only running air conditioning during the hours or days you are in the shop. An air conditioner typically needs to run for at least a few days without interruption before it has a chance to stabilize the overall humidity level. Intermittent usage patterns do not typically result in favorable humidity levels but results can vary.

Even when one runs their air conditioning full time a dehumidifier may still be needed in a shop to bring humidity levels down to more comfortable levels (which often allows the A/C temp to be turned up a few degrees higher). It all depends upon whether your A/C can get the humidity level down to about 50%RH. Even if it does, it will only do so if there is a call for it to run, on cooler days the humidity will once again be uncontrolled unless heating is called for, but a dehumidifier will always keep the humidity under control, except if your shop gets too cold (some units have a minimum operating temperature), but high humidity is not a common issue in winter.

As for which condensate pump I am using, it was whatever condensate pump Lowes was selling at the time (in the same section as their dehumidifies aisle). They are also available online and are often used with dehumidifier sand air conditioning units.

Sealing the floor will help only if it is a significant source of moisture, and that all depends upon the concrete mixture used when the floor was poured. You can tape down clear Saran wrap to a section of your floor (exterior walls tend to have more moisture), taking care to seal the edges with the tape. Keep an eye out for the buildup of visible moisture (water droplets or condensate) on the Saran. If after a week or so of observation the area is still substantially dry then sealing will contribute little benefit. It is best if there has been some recent rain to ensure the ground is moist do the test can work.

 

[Alex Stokes]

Many thanks Ethan - I'm off to get this sorted out!